Hydrometallurgical process



Patented Jan. 30, 1940 UNITED STATES HYDROMETALLURGICAL PROCESS ThomasA. Campbell, Chuquicamata, Chile, as-

signor to Chile Exploration Company, New York, N. Y., a corporation ofNew Jersey No Drawing. Application October 29, 1937, Serial No. 171,686.In Chile June 15, 1937 11 Claims.

This invention relates to hydrometallurgical processes. Moreparticularly, the invention relates to hydrometallurgical processesinvolving the use of electrolytes containing a colloidally 6 dispersedcompound of molybdenum, and has for its principal object the provisionof an improved method ior the treatment of such electrolytes for thepurpose of increasing their stability. In accordance with the method ofthe 10 invention, colloidally dispersed compounds of 'molybdenum areseparated from electrolyte solutions in which they are present, and theseparated molybdenum compound may be recovered in marketable form.

16 The presence of colloidally dispersed compounds of molybdenum incertain electrolytes is objectionable. This is true especially in thecase of electrolytes employed in hydrometallurgical (and other)processes involving oxidation or 90 reduction reactions, becausemolybdenum compounds in colloidal form are susceptible to oxidation andreduction and interfere with eflicient progress of the oxidation andreduction reactions sought to be carried out. For example,

35 the presence of colloidally dispersed molybdenum compounds in thecopper-bearing electrolytes employed in hydrometallurgical processesdesigned for the recovery of copper is objectionable both duringpurification or the electrolyte 30 and during treatment of the purifiedelectrolyte for the recovery of its copper content. The reactionsoccurring at these stages in the treatment of such electrolytes involveoxidation and reduction reactions the-progress of which is im- 35 pededby the presence of colloidally dispersed molybdenum compounds.

In the recovery .of copper from an oxidized copper ore, the ore isleached with a solution containing sulphuric acid'to obtain a solution40 containing copper sulphate. The resulting copper sulphate solutionalso contains impurities such as nitrates and chlorides and sulphate ofiron, and to eliminate certain of these impurities, particularly thechlorides, and to reduce 45 others, especially the iron, the solution issubjected to a reducing or dechloridizing operation in the presence ofmetallic copper. If molybdenum is. present in the solution during thisdechloridizing operation, it is reduced to the form of a hydrated oxidecorresponding to the formula M03Oa-5H2O. This hydrated oxide ofmolybdenum is colored a deep blue and appears in the electrolyte in theform of a colloid. It is ex- 55 tremely sensitive to oxidation and actsas a reducer of nitric acid in. solution, thereby itself becomingoxidized. Such a reaction sets in operation a train of oxidation andreduction reactions involving nitric acid, iron and molybdenum andrendering the solutionunstable and highly I. corrosive to copper.'Cathodes being deposited from such a solution are attacked and corrodedbythe solution. Moreover, cement copper, added to such a solution forthe purpose of precipitating chlorides as cuprous chloride and for 19reducing ferric iron in solution, is attacked by the colloidallydispersed molybdenum and its efiectiveness as an agent for accomplishingthe purposes for which it is added is thereby diminished. As a result,the efliciency of the entire process for the recovery of copper isimpaired.

It has been found that colloidal molybdenum compounds present insolutions such as described above carry a negative charge, and that bysubjecting the electrolyte to a precipitation operation in the presenceof -a substance capable of. efiecting precipitation of the colloidallydispersed molybdenum compound, .the molybdenum compound is precipitatedin a form that is easily 3;;

separated from the residual electrolyte. The precipitation may beeffected byincorporating in the electrolyte containing the colloidalmolybdenum compound a suitable colloid carrying a positive charge such,for example, as glue, orby the addition of a suitable coagulating agent,such, for example, as activated carbon. Upon precipitation of thecolloidal molybdenum compound, for example, by means of glue, theresulting formed precipitatesettles quickly from the solution and iseasily separated therefrom. The precipitate is composed of glue ordecomposition products of glue, molybdenum oxide, impurities such assilica, and small amounts of substances included in entrainedelectrolyte. The precipio tate contains the molybdenum in fairlyconcentrated form, and it is easily converted to a marketable molybdenumproduct.

As illustrative of the manner in which the method of the invention iscarried out, it is described below in connection with the treatment ofan electrolyte employed in the hydrometallurgical treatment of oxidizedcopper ores for the recovery of copper. The copper .ore is leached witha solution containing sulphuric acid, usually in the form of spentelectrolyte from the electrolytic cells in which metallic copper isrecovered, and the copper sulphate solution (or elec trolyte) thusobtained ordinarily .contains the following ingredients about in theconcentration ranges indicated:

Grams per liter Copper 20 to '70 Sulphuric acid 70 to 5 Nitric acid toIron to 10 Molybdenum to 8 Chlorine "45 to In addition, the electrolytemay contain impurities such as sodium, potassium, lead, tin, aluminum,managanese, selenium, tellurium, arsenic and antimony. The presence orabsence of these impurities, however, does not appear to have anyinfluence on the effectiveness of the method of the invention. Themolybdenum, at this stage of the process, is in true solution in theelectrolyte.

The electrolyte from the leaching operation is introduced into asuitable urification vessel and is agitated in the presence of areducing agent such as cement copper. The primary function of the copperis to reduce the iron in solution to the ferrous form and to efiectelimination of the bulk of the chlorides by precipitation as cuprouschloride. In addition, however, the copper eifects conversion ofmolybdenum in the solution to the form of a hydrated molybdenum oxidecorresponding to the formula.

MO30s-5H20, which appears in colloidal form in the electrolyte. Theoccurrence of the reaction by which this colloidal molybdenum compoundis formed does not depend upon the presence or absence of coppersulphate or sulphuric acid. Substantially the same colloidal molybdenumcompound is formed whenever a reducing reagent such as copper is broughtin contact with a solution containing molybdenum in oxidized form,whether or not the solution also contains copper sulphate or sulphuricacid.

The metallic copper employed as the reducing material is separated fromthe electrolyte, and a suspension of glue in water is incorporated inthe resulting reduced electrolyte containing the colloidally dispersedmolybdenum compound. The strength of the glue suspension and the amountthat is employed depends upon the amount of colloidally dispersedmolybdenum compound in the electrolyte undergoing treatment. Preferablythe electrolyte is agitated during incorporation of the gluesuspensionin order to efiect thorough dissemination of the glue throughout theelectrolyte. The glue brings about precipitation of the colloidalmolybdenum compound in a form that is easily separated from theelectrolyte.

To efiect separation of the thus precipitated molybdenum compound fromthe residual electrolyte, the electrolyte is introduced into a suitablesettling or thickening vessel. In the settling or thickening vessel, theprecipitate settles accompanying electrolyte.

The separated precipitate contains molybdenum in the form of an oxidethat is easily treated toconvert it to a marketable molybdenum product.

The electrolyte, after separation of the precipitate, is introduced intoan electrolytic cell where it is electrolyzed in the usual manner forthe recovery of its copper content. The spent electrolyte from theelectrolyzing operation is returned to the leaching operation for thepurpose Of utilizing its sulphuric acid content in the extraction ofcopper from a further quantity of ore.

It has been found that the electrolyzing operation proceeds moreefliciently when employing as the electrolyte a solution from whichmolybdenum has been separated in the manner described above than when anelectrolyte from which molybdenum has not been removed is employed. Ithas also been found that in a cyclic operation such as described above,the treatment of the electrolyte for the elimination of the molybdenumlowers the molybdenum content of all of the electrolyte employed in theprocess and thereby increases the eificiency with which the purificationoperation preceding the molybdenum precipitation operation proceeds. Themethod of the invention, therefore, contributes materially to theefiiciency and economy of the copper recovery process.

Various modifications may be made in carrying out the process of theinvention. As it has been described above, the process of the inventioninvolves the use of glue as the agent capable of effecting precipitationof the colloidal molybdenum compound, but other agents are available foraccomplishing this purpose, such, for example, as activated carbon. Thespecific process described above for the recovery of copper from copperores involves the use of metallic copper as the reducing materialemployed in purifying the electrolyte solution and in effectingconversion of the molybdenum in solution to the form of a colloidallydispersed compound of molybdenum, but other reducing agents, such assulphur dioxide either in gaseous or in liquid form, may be employed,either alone or in combination with metallic copper.

It is apparent that the method of the invention, although particularlywell adapted to use in connection with hydrometallurgical processes forthe treatment of copper ores, is not limited in its utility to suchprocesses. It may be employed equally well in other processes where itis desired to increase the stability of electrolytes rendered unstableby the presence of molybdenum, and may be employed also in processes forthe recovery of molybdenum from solutions in which it is present.

I claim:

1. In a hydrometallurgical process for the recovery of copper in whichan oxidized copper ore is leached with sulphuric acid and a solutioncomprising copper sulphate and containing a colloidally dispersedmolybdenum compound is obtained, the improvement which comprisessubjecting the copper sulphate solution to a precipitation operation inthe presence of activated carbon to effect precipitation of thecolloidally dispersed molybdenum compound, agitating the solution duringthe course of the precipitation operation, and separating theprecipitated molybdenum compound from the residual solution.

2. A hydrometallurgical process for the recovery of copper from anoxidized copper ore area-17a containing molybdenum which comprisesleaching the ore with a solution containing sulphuric acid to obtain asolution containing copper sulphate and dissolved molybdenum, subjectingthe resulting copper sulphate solution to a reducing operation in thecourse of which the dissolved molybdenum is converted to the form of acolloidally dispersed compound of molybdenum, thereafter subjecting thesolution to the action of a substance capable of efiecting precipitationof the colloidally dispersed compound of molybdenum, thereby toprecipitate the molybdenum compound, separating the precipitatedmolybdenum compound from the solution, and treating the resultingclarified solution for the recovery of its copper content.

3. A hydrometallurgical process for the recovery of copper from anoxidized copper ore containing molybdenum and iron which comprisesleaching the ore with a solution containing sulphuric acid to obtain asolution containing copper sulphate, dissolved molybdenum, and ferriciron, subjecting the resulting copper sulphate solution to the action ofmetallic copper to reduce the ferric iron to the ferrous form and toconvert the dissolved molybdenum to the form of a colloidally dispersedcompound of molybdenum, thereafter subjecting the solution to the actionof activated carbon to effect precipitation of the colloidally dispersedcompound of molybdenum, separating the precipitated molybdenum compoundfrom the solution, and subjecting the resulting clarified solution to anelectrolytic operation for the recovery of its copper content.

4. A hydrometallurgical process for the recovery of copper from anoxidized copper ore containing molybdenum and iron which comprisesleaching the ore with a solution containing sulphuric acid to obtain asolution containing copper sulphate, dissolved molybdenum, and ferriciron, subjecting the resulting copper sulphate solution to the action ofsulphur dioxide to reduce the ferric iron to the ferrous form and toconvert the dissolved molybdenum to the form of a colloidally dispersedcompound of molybdenum, thereafter subjecting the solution to the actionof activated carbon to efiect precipitation of the colloidally dispersedcompound of molybdenum, separating the precipitated molybdenum compoundfrom the solution, and subjecting the resulting clarified solution to anelectrolytic operation for the recovery of its copper content.

5. The method of increasing the stability of a copper sulphateelectrolyte containing nitric acid, dissolved iron, and a colloidallydispersed compound of molybdenum which comprises subjecting theelectrolyte to the action of activated carbon to efiect precipitation ofthe colloidally dispersed molybdenum compound, and separating theprecipitated .molybdenum compound from the electrolyte.

6. The method of recovering molybdenum from solutions containing acolloidally dispersed compound of molybdenum which comprises subjectingthe solution to the action of glue to effect precipitation of themolybdenum compound, separating the precipitated molybdenum compoundfrom the residual solution, and-treating the separated precipitate forthe recovery of its molybdenum content.

7. The method of recovering molybdenum from copper sulphate solutionscontaining dissolved molybdenum which comprises subjecting the solutionto the action of a reducing agent to convert the molybdenum to the formof a colloidally dispersed compound of molybdenum, subjecting theresulting solution to the action of a substance capable of effectingprecipitat on of the colloidally dispersed compound of molybdenum,thereby to precipitate the molybdenum compound, and separating theprecipitated molybdenum compound from the residual solution.

8. The method of recovering molybdenum from a sulphate solutioncontaining dissolved molybdenum which comprises treating the solutionwith a reducing agent of the class consisting of cement copper andsulphur dioxide to convert the molybdenum to the form of a colloidallydispersed compound of molybdenum, subjecting the resulting solution ofthe actions of a substance capable of effecting precipitation of thecolloidally dispersed compound of molybdenum, there! by to precipitatethe molybdenum compound, and separating the precipitated molybdenumcompound from the residual solution.

9. The method of recovering molybdenum from a solution of a copper saltcontaining dissolved molybdenum which comprises treating the solutionwith a reducing agent of the class consisting of cement copper andsulphur dioxide to convert the molybdenum to the form of a colloidallydispersed compound of molybdenum,

subjecting the resulting solution to the actionsof a substance capableof efiecting precipitation of the colloidally dispersed compound ofmolybdenum, thereby to precipitate the molybdenum compound, andseparating the precipitated molybdenum compound from the residualsolution.

10. The method of recovering molybdenum as set forth in claim 8 in whichthe agent for precipitating the colloidally dispersed molybdenumcompound is activated carbon.

11., The method of recovering molybdenum as set forth in claim 9 inwhich the agent for precipitating the colloidally. dispersed molybdenumcompound is activated carbon..

THOMAS A. CAIMPBEIL.

